Atomic layer deposition bonding for heterogeneous integration of photonics and electronics

ABSTRACT

Methods and systems are presented for heterogeneous integration of photonics and electronics with atomic layer deposition (ALD) bonding. One method includes operations for forming a compound semiconductor and for depositing (e.g., via atomic layer deposition) a continuous film of a protection material (e.g., Al2O3) on a first surface of the compound semiconductor. Further, the method includes an operation for forming a silicon on insulator (SOI) wafer, with the SOI wafer comprising one or more waveguides. The method further includes bonding the compound semiconductor at the first surface to the SOI wafer to form a bonded structure and processing the bonded structure. The protection material protects the compound semiconductor from acid etchants during further processing of the bonded structure.

TECHNICAL FIELD

The subject matter disclosed herein generally relates to methods andsystems for semiconductor manufacturing and, more specifically, tosemiconductor manufacturing that includes bonding of heterogeneousmaterials.

BACKGROUND

Heterogeneous bonding of two different types of materials is becomingmore common in optics and electronics for manufacturing integratedcircuits (IC). The combination takes advantage of using materials withspecialized and different properties to be combined into a singlesemiconductor for processing.

For example, a silicon on insulator (SOI) wafer provides low losswaveguide routing while a III-V compound semiconductor generates lightefficiently for lasers, and absorbs light efficiently for modulators anddetectors used in optical communication. The combination of thesematerials provides an ideal platform for creating photonic integratedcircuits (PICs). Since the materials are dissimilar, the bond greatlyinfluences the yield and process limitation in making these PICs. Forexample, in some applications, the goal is to make a highly integratedtransmitter that is completely made through wafer-level scaleprocessing.

For hybrid Si photonics, the shear strength of the bond between thecompound semiconductor to the Si substrate has a great impact of deviceyield. Since the materials being bonded are different, separation anddelamination between the materials is a common challenge to overcome. Inaddition, a multitude of acids are used in the fabrication of thesedevices to etch the compound semiconductor after bonding. However, theacids wick underneath the compound semiconductor following the Sichannels and etch the bonding interface.

BRIEF DESCRIPTION OF THE DRAWINGS

Various ones of the appended drawings merely illustrate exampleembodiments of the present disclosure and cannot be considered aslimiting its scope.

FIG. 1 illustrates the bonding of heterogeneous materials, according tosome example embodiments.

FIG. 2 illustrates the damage to the compound semiconductor due to acidutilized during the processing of the bonded structure, according tosome example embodiments.

FIG. 3 illustrates the addition of a protection material via atomiclayer deposition (ALD), according to some embodiments.

FIG. 4 illustrates the creation of a bonded structure by bonding thecompound semiconductor and the SOI wafer, according to some exampleembodiments.

FIG. 5 illustrates a compound structure without a super lattice,according to some example embodiments.

FIG. 6 shows how the Al₂O₃ enhanced bonded structure provides betterprotection during processing, according to some example embodiments.

FIG. 7 illustrates some results showing the improvement obtained byutilizing the protection layer, according to some example embodiments.

FIG. 8 illustrates the yield improvement gains obtained with the Al₂O₃layer, according to some embodiments.

FIG. 9 is a flowchart of a method for heterogeneous integration ofphotonics and electronics with ALD bonding.

FIG. 10 is a flowchart of a method for making a bonded structure,according to some example embodiments.

DETAILED DESCRIPTION

Example methods and systems are directed to for heterogeneousintegration of photonics and electronics with atomic layer deposition(ALD) bonding. Examples merely typify possible variations. Unlessexplicitly stated otherwise, components and functions are optional andmay be combined or subdivided, and operations may vary in sequence or becombined or subdivided. In the following description, for purposes ofexplanation, numerous specific details are set forth to provide athorough understanding of example embodiments. It will be evident to oneskilled in the art, however, that the present subject matter may bepracticed without these specific in details.

The bonded structure has problems that must be addressed duringmanufacturing, such as the bonding shear strength and acid damage inpost-bonding processing. Some solutions solve these problems by changingthe bond layer of the III-V semiconductor to InGaAsP, which is moreresistant to many acid etches. However, this change also reduces theshear strength and leads to delamination prior to the acid steps. Othersolutions include changes to the acid etch steps, the device artwork, orthe setback from the III-V edge to the III-V devices. However, thesesolutions do not increase the shear strength of the bonding, they addprocessing time and cost, and they do not fully solve the problem ofacid wicking. Further, these solutions do not allow the setback from theIII-V edge to the device to be reduced, thereby limiting the shrinkingof the die size.

Embodiments presented herein provide solutions for bonding an SOI waferwith a compound semiconductor (e.g., a semiconductor formed on III-Vmaterials). Embodiments provide for adding a thin layer of protectionmaterial (e.g., Al₂O₃) to the bonding surface in the compoundsemiconductor (e.g., III-V based) after growth and prior to the bondingoperation. In some examples, the addition of the thin layer is performedvia ALD, but other deposition methods may be utilized. The Al₂O₃protects the III-V material from acid etchants after bonding and alsoincreases the shear strength of the bond (e.g., compared to SiO₂). Inaddition, the protection material results in fewer defects, higheryields, and provides the ability to make smaller optical circuits whileusing less material.

One general aspect includes a method including operations for forming acompound semiconductor, depositing a continuous film of a protectionmaterial on a first surface of the compound semiconductor, and forming aSOI wafer, with the SOI wafer including one or more waveguides. Themethod also includes bonding the compound semiconductor at the firstsurface to the SOI wafer to form a bonded structure and processing thebonded structure. The protection material protects the compoundsemiconductor from acid etchants during the processing of the bondedstructure.

One general aspect includes a bonded structure including a compoundsemiconductor, including a continuous film of a protection materialdeposited on a first surface of the compound semiconductor, and a SOIwafer. The SOI wafer includes one or more waveguides, where the compoundsemiconductor is bonded at the first surface to the SOI wafer to formthe semiconductor structure, the bonded structure being processable topattern circuits on the compound semiconductor. The protection materialprotects the compound semiconductor from acid etchants during theprocessing of the bonded structure.

One general aspect includes a method including operations for forming aIII-V based semiconductor, depositing a continuous film of Al₂O₃ on afirst surface of the III-V based semiconductor, singulating the III-Vbased semiconductor to create epi dies, and plasma cleaning the epidies. The method further includes operations for forming a SOI wafer,with the SOI wafer including one or more waveguides, placing the firstsurface of the epi dies on the SOI wafer, bonding the epi dies to theSOI wafer to form a bonded structure, removing a substrate of the epidie through grind and chemical operations, and processing the bondedstructure, where the Al₂O₃ protects the epi dies from acid etchantsduring the processing of the bonded structure.

FIG. 1 illustrates the bonding of heterogeneous materials, according tosome example embodiments. FIG. 1 shows a cross-section of a compoundsemiconductor 102 and an SOI wafer 104 before being bonded together. TheSOI wafer 104, or silicon-on-insulator wafer, is created with a siliconbase 120, a layer of SiO₂ 118 on top of the silicon base 120, and asilicon waveguide 122 that provides low-loss routing. In addition, aSiO₂ bonding layer 116 is added on top of the waveguide 122. The SOIwafer is made by forming and patterning the silicon waveguides, and thenthe SOI wafer is plasma cleaned. For simplicity of description, otherlayers and circuits in the SOI wafer are omitted, but a person skilledin the art would readily appreciate that the SOI wafer may include aplurality of circuits and layers.

Further, a compound semiconductor 102 is grown separately. In someexample embodiments, the compound semiconductor 102 utilizes III-V typematerials, a class of materials which produce efficient lasers,modulators, and detectors.

In some example embodiments, the compound semiconductor 102 includes abase of InP substrate and additional layers are added. In the exampleembodiment of FIG. 1, the layers include a InGaAs layer 110, another InPlayer, a QWs layer 112, another InP layer 114, a super lattice 106, andan InP bond layer 108.

It is noted that a large III-V semiconductor may be formed and thensingulated into a plurality of epi dies prior to bonding. The epi diesare referred to herein as the compound semiconductor 102, and the epidies are bonded to the SOI wafer.

The combination of the compound semiconductor 102 and the SOI wafer 104is desired because the silicon provides the low-loss waveguide routingand the III-V materials provide efficient light properties. Because theyare different types of materials, the compound semiconductor 102 and theSOI wafer 104 are bonded together. Different oxide types of bondingmaterials may be used to connect the two semiconductors together.

In some example embodiments, the compound semiconductor 102 and the SOIwafer 104 are placed together and then pressure and heat are applied tobond them together. Afterwards, they may be plasma cleaned and furthersteps may be taken to form circuits on the compound semiconductor 102.That is, at this point, the silicon patterning is done, but the III-Vpatterning is still in progress. In other bonding approaches, a polymer(e.g., benzocyclobutene, commonly abbreviated as BCB) bond is used, suchthat the III-V is connected to the silicon using the polymer.

It is noted that the embodiments illustrated in FIG. 1 are examples anddo not describe every possible embodiment. Other embodiments may utilizedifferent, additional, or fewer layers on the compound semiconductor 102and the SOI wafer 104. The embodiments illustrated in FIG. 1 shouldtherefore not be interpreted to be exclusive or limiting, but ratherillustrative.

FIG. 2 illustrates the damage to the compound semiconductor due to acidutilized during the processing of the bonded structure, according tosome example embodiments. After the two semiconductors are bondedtogether, additional processing of the compound semiconductor 102 takesplace. Some operations may include using acid to edge the compoundsemiconductor substrate 202 to reduce compound semiconductor thickness.

However, when using acid, the acid may edge at the bottom 204 of thecompound semiconductor 102 or may create damage along the Si waveguide122. Because there is damage 204 at the edge, the edges have to beremoved, which limits how small the semiconductors may be.

FIG. 3 illustrates the addition of a protection material via ALD 304,according to some embodiments. In some example embodiments, a thin filmof protection material 306 is deposited using ALD 304 on the compoundsemiconductor 102, resulting in compound semiconductor 302 withprotection material 306. Atomic layer deposition (ALD) is a thin filmdeposition technique that is based on the sequential use of a gas phasechemical process. ALD is considered a type of chemical vapor deposition.A majority of ALD reactions use two chemicals, typically calledprecursors. These precursors react with the surface of a material one ata time in a sequential, self-limiting, manner. Through the repeatedexposure to separate precursors, a thin film is slowly deposited.

Embodiments are presented herein by using Al₂O₃ as the protectionmaterial, but other dielectric materials may be used, such as SiO₂,HfO₂, ZrO₂, SiN, TiO₂, or other dielectric films. In addition, ALD isused for describing the present embodiments, but other depositionmethods may be used instead, such as plasma enhanced chemical vapordeposition (PECVD), ion beam deposition (IBD), and radio frequency (RF)sputtering.

The height of the deposition layer is in the range of 1 to 50nanometers, although other values are also possible. In some exampleembodiments, a 10 nm layer is utilized.

One of the advantages of using ALD is that it improves the shearstrength of the bond because, among other reasons, it provides avirtually defect free layer that is better suited for bonding. The ALDfilms are completely conformal in that there are no breaks in the filmsand no discontinuities. It is also easy to control the thickness of thefilm so that the layer may be as small as a single monolayer(approximately a nanometer) and all the way up to tens or hundreds ofnanometers. The results from using Al₂O₃ deposited with ALD is that thebond quality is greatly improved.

FIG. 4 illustrates the creation of a bonded structure by bonding thecompound semiconductor and the SOI wafer, according to some exampleembodiments. After the Al₂O₃ is deposited, the compound semiconductor302 and the SOI wafer 104 are bonded together to create a bondedstructure 304. For example, the two semiconductors may be bondedtogether by placing them together and then applying pressure and heat.

The bond forms oxides on the III-V and oxides on the silicon, and theoxides keep the compound semiconductor 302 and the SOI wafer 104connected.

FIG. 5 illustrates a compound structure without the super lattice,according to some example embodiments. A disadvantage of incorporatingthe Al₂O₃ on the compound semiconductor is that the separation of theIII-V from the Si waveguide is increased. The optical operations in thePIC need to transfer an optical mode (i.e. light) from one material tothe other; therefore, reducing this separation is desirable.

In the photonic integrated circuits, the light is routed around the chipin silicon waveguides, and then the active optical functions, such aslasers, detectors and modulators, take place in the III-V material.Therefore, in an active device, there is a coupling between the siliconand the III-V. The Al₂O₃ adds thickness to the gap between the siliconand the III-V, so the performance of the coupling is decreased. Thesmaller the gap between the silicon and the active layer of the III-V,the better the coupling between the two materials.

In some example embodiments, the solution is to decrease the distance ofthe optical coupling, such as by eliminating the super lattice in thecompound semiconductor 502. A super lattice includes two materials whichare grown one after the other in very thin layers. For example, thesuper lattice layers may be around 10 nm while other layers may be inthe tens or hundreds of nanometers. The purpose of the super lattice isto prevent defects from moving from the bottom surface up into thematerial. The super lattice layer acts as a defect block mechanism andimproves the reliability of the device. The removal of the super latticemakes the compound semiconductor at risk from bond defects, yet it alsoimproves coupling performance between the Si and compound semiconductor.

However, the Al₂O₃ layer provides similar protection by moving the bondinterface away from the compound semiconductor surface, therefore somedefect blocking is maintained even after removing the super lattice.Meanwhile, the distance (i.e. optical confinement) from the III-V to thesilicon waveguide is reduced improving coupling performance, and thequality of the bonding is also improved. Removing the super lattice is atrade-off, but overall the performance is better with the Al₂O₃ layer.

In simulations, the detector responsivity and modulator insertion losswere better with the 10 nm Al₂O₃ layer and without the super latticecompared to the compound semiconductor having the super lattice but noAl₂O₃ layer.

FIG. 6 shows how the Al₂O₃ enhanced bonded structure provides betterprotection during processing, according to some example embodiments.After adding the Al₂O₃ 306 to the compound structure 502, it wasobserved that the damage from acid utilized during etching 602operations was greatly reduced. The damage was reduced on the edges ofthe compound semiconductor as well as along the silicon waveguide.

In some laboratory tests, and cited as an example without meaning to belimiting, the observed damage at the edges with a 10 nm layer of Al₂O₃were practically eliminated. At 2 nm and at 5 nm some damage at the edgewas observed, but the damage was less than without using the Al₂O₃layer. Further, the shear strength of the bonding was also improved.More sample results are provided below with reference to FIG. 7.

FIG. 7 illustrates some results showing the improvement obtained byutilizing the protection layer, according to some example embodiments. Afew tests were performed for semiconductors with and without Al₂O₃ andthe damage on the edges of the bond were measured.

Capture 702 illustrates an image taken of a bonded structure without ALDAl₂O₃, and capture 704 illustrates an image taken of a bonded structurewith ALD Al₂O₃ 10 nm thick. Capture 702 shows that there is damage atthe edge of the bonding because there is material missing, while thebonded structure with the ALD Al₂O₃ shows no observable damage. Theedges of the ALD Al₂O₃ were continuous and undamaged, and there was nounder-etch.

The shear strength was also measured by checking the amount of forceneeded to separate the bonded structures. In some tests, the shearstrength of the ALD Al₂O₃ semiconductor was about two and a half timesthe shear strength of the semiconductor without the Al₂O₃.

In other tests, the performance of the detector regarding lightresponsivity was measured for different semiconductor structures. Sincethe super lattice had been eliminated from the compound structure, thelight responsivity was improved because the Al₂O₃ layer was thinner thanthe super lattice, resulting in a closer light coupling.

FIG. 8 illustrates the yield improvement gains obtained with Al₂O₃layer, according to some embodiments. The benefits of the ALD Al₂O₃semiconductor include: (a) reduced, or eliminated, plasma cleaningrequired on the III-V piece prior to bonding, which allows higherthroughput; (b) smaller pieces of III-V may be bonded since the setbackfrom III-V edge to device may be reduced; (c) reduced die size and moredie per wafer, since the die size is limited currently by the III-V bondpiece size; and (d) greatly reduced III-V surface defect growth afterbonding.

Device 802 is a semiconductor circuit bonded without the use of Al₂O₃.The device 802 includes four pieces of compound semiconductor 806 bondedon top of the SOI wafer. Because of the damage on the edges of thecompound semiconductor 806, only a reduced portion 808 may be used forthe final PIC.

Device 804 includes four compound semiconductors 810 bonded on top ofthe SOI wafer. Because the compound semiconductor 810 is not damaged dueto the protection provided by the Al₂O₃ layer, the complete compoundsemiconductor may be utilized for the PIC.

It is also noted that because the compound semiconductors are notdamaged, it is possible to place the III-V pieces closer together, whichresults in smaller PICs and improved III-V usage, resulting in lesswaste and less cost for the III-V semiconductor. Further, since there isless waste on the III-V semiconductor, there is also less waste on theSOI wafer, resulting in reduced silicon expenses.

In some examples, it is possible to use simpler manufacturing processesbecause the compound semiconductor is not as sensitive to acidchemicals.

FIG. 9 is a flowchart of a method 900 for heterogeneous integration ofphotonics and electronics with ALD bonding. At operation 902, thecompound semiconductor material is grown, and at operation 904, theprotection material is deposited on the compound semiconductor grown inoperation 902. In some example embodiments, the deposition is performedutilizing ALD and the protection material is Al₂O₃, although otherprotection materials are also possible.

At operation 906, the III-V wafer is then singulated into small piecesfor bonding to the SOI wafer. The epi die are plasma cleaned atoperation 908, ensuring that the surface is very clean before bonding.

At operation 910, the SOI wafer is patterned and fabricated, includingthe silicon waveguides, and the SOI wafer is plasma cleaned at operation912.

At operation 914, the epi die are placed on the SOI wafer surface, andat operation 916, pressure and heat are applied to the epi die on top ofthe SOI wafer to improve the bond.

From operation 916, the method flows to operation 918, where the epi diesubstrate is removed through grinding and chemical etch steps (with theimproved performance provided by the protection material layer). Atoperation 920, additional steps are performed on the heterogeneouslybonded structure for epi die and device patterning.

FIG. 10 is a flowchart of a method 1000 for making a bonded structure,according to some example embodiments. While the various operations inthe flowcharts of FIGS. 9 and 10 are presented and describedsequentially, one of ordinary skill will appreciate that some or all ofthe operations may be executed in a different order, be combined oromitted, or be executed in parallel.

At operation 1002, the compound semiconductor is formed (e.g., compoundsemiconductor 502 of FIG. 5). From operation 1002, the method flows tooperation 1004 where a continuous film of a protection material (e.g.,Al₂O₃ layer 306 of FIG. 5) is deposited on a first surface of thecompound semiconductor.

Further, at operation 1006, a SOI wafer is formed (e.g., SOI wafer 104of FIG. 5), with the SOI wafer comprising one or more waveguides 122.From operation 1006, the method flows to operation 1008 for bonding thecompound semiconductor at the first surface to the SOI wafer to form abonded structure.

From operation 1008, the method flows to operation 1010 for processingthe bonded structure. The protection material protects the compoundsemiconductor from acid etchants during the processing of the bondedstructure.

In one example, depositing the continuous film is performed by atomiclayer deposition.

In some examples, the protection material is Al₂O₃. In other examples,the protection material is one of SiO₂, HfO₂, ZrO₂, SiN, or TiO₂.

In some examples, the continuous film has a height between 2 and 50nanometers, but other heights of the protection layer are possible, suchas in the range from 1 to 100 nanometers.

In some example embodiments, the compound semiconductor is a III-Vwafer.

In some example embodiments, bonding the compound semiconductor to theSOI wafer further includes placing the compound semiconductor on the SOIwafer, applying pressure and heat to the compound semiconductor and theSOI wafer, and removing the pressure and heat.

In some examples, the SOI wafer includes a SiO₂ layer directly above oneof the one or more waveguides, where the SiO₂ layer is placed in contactwith the first surface of the compound semiconductor for the bonding.

In some examples, the compound semiconductor does not include a superlattice layer to compensate for the increased sized of the compoundsemiconductor with the continuous film of the protection material.

In some examples, processing the bonded structure further includesremoving an epi substrate from the compound semiconductor through grindand chemical steps and device patterning on the compound semiconductor.

Throughout this specification, plural instances may implementcomponents, operations, or structures described as a single instance.Although individual operations of one or more methods are illustratedand described as separate operations, one or more of the individualoperations may be performed concurrently, and nothing requires that theoperations be performed in the order illustrated. Structures andfunctionality presented as separate components in example configurationsmay be implemented as a combined structure or component. Similarly,structures and functionality presented as a single component may beimplemented as separate components. These and other variations,modifications, additions, and improvements fall within the scope of thesubject matter herein.

The embodiments illustrated herein are described in sufficient detail toenable those skilled in the art to practice the teachings disclosed.Other embodiments may be used and derived therefrom, such thatstructural and logical substitutions and changes may be made withoutdeparting from the scope of this disclosure. The Detailed Description,therefore, is not to be taken in a limiting sense, and the scope ofvarious embodiments is defined only by the appended claims, along withthe full range of equivalents to which such claims are entitled.

As used herein, the term “or” may be construed in either an inclusive orexclusive sense. Moreover, plural instances may be provided forresources, operations, or structures described herein as a singleinstance. Additionally, boundaries between various resources,operations, modules, engines, and data stores are somewhat arbitrary,and particular operations are illustrated in a context of specificillustrative configurations. Other allocations of functionality areenvisioned and may fall within a scope of various embodiments of thepresent disclosure. In general, structures and functionality presentedas separate resources in the example configurations may be implementedas a combined structure or resource. Similarly, structures andfunctionality presented as a single resource may be implemented asseparate resources. These and other variations, modifications,additions, and improvements fall within a scope of embodiments of thepresent disclosure as represented by the appended claims. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

What is claimed is:
 1. A method comprising: forming a compoundsemiconductor; depositing a film of protection material on a side of thecompound semiconductor using vapor deposition; forming a silicon oninsulator (SOI) wafer, the SOI wafer comprising one or more waveguides;forming a bonded structure by placing the side of the compoundsemiconductor on the SOI wafer and applying heat, the side of thecompound semiconductor placed such that the film of protection materialis in contact with the SOI wafer; applying acid etchants to the bondedstructure, the protection material protecting the side of the compoundsemiconductor from the acid etchants.
 2. The method as recited in claim1, wherein the vapor deposition used to deposit the film of theprotection material is atomic layer deposition.
 3. The method as recitedin claim 1, wherein the protection material is Al₂O₃.
 4. The method asrecited in claim 1, wherein the compound semiconductor is bonded to abonding surface of the SOI wafer, and wherein the protection materialprotects the bonding surface of the SOI wafer from the acid etchants. 5.The method as recited in claim 1, wherein the film has a height between2 and 50 nanometers.
 6. The method as recited in claim 1, wherein thecompound semiconductor is a III-V wafer.
 7. The method as recited inclaim 1, wherein bonding the compound semiconductor to the SOI waferfurther comprises: placing the compound semiconductor on the SOI wafer;applying pressure and the heat to the compound semiconductor and the SOIwafer; and removing the pressure and the heat.
 8. The method as recitedin claim 1, wherein the SOI wafer includes a SiO₂ layer directly aboveone of the one or more waveguides, wherein the SiO₂ layer is placed incontact with the side of the compound semiconductor for the bonding. 9.The method as recited in claim 1, wherein the compound semiconductordoes not include a super lattice layer.
 10. The method as recited inclaim 1, wherein the applied acid etchants pattern a circuit on thecompound semiconductor.
 11. A method comprising: forming a III-V basedsemiconductor; layering a film of Al₂O₃ on sides of the III-V basedsemiconductor; singulating the III-V based semiconductor to create aplurality of dies; plasma cleaning the plurality of dies; forming asilicon on insulator (SOI) wafer, the SOI wafer comprising one or morewaveguides; placing the sides of the plurality of dies on the SOI wafersuch that the film is in contact with the SOI wafer; bonding, byapplying heat, the plurality of dies to the SOI wafer to form a bondedstructure; and applying acid etchants to the bonded structure, the Al₂O₃protecting the sides of the plurality of dies from the acid etchants.12. The method as recited in claim 11, wherein depositing the film ofAl₂O₃ is performed by atomic layer deposition.
 13. The method as recitedin claim 11, wherein bonding the plurality of dies to the SOI waferfurther comprises: applying pressure and heat to the plurality of diesand the SOI wafer; and removing the pressure and heat.
 14. The method asrecited in claim 11, wherein the SOI wafer includes a SiO₂ layerdirectly above one of the one or more waveguides, wherein the SiO₂ layeris placed in contact with the sides of the plurality of dies.